Download Lab M14 – Pulleys

Lab M14 – Pulleys
PH306 10/16/07
Name___________________________
Partner_________________________
Goal
To learn about the relationships between effort and load forces and distances for pulleys.
Prelab
Complete the handout “Prelab Problem for Pulley Activity.”
Procedure
Measure and record all forces as accurately as possible. Use the smallest division on your scale, and
estimate any fractions of a division.
1. Following the diagram on CP p. 113, set up a pulley system that has 2 pulleys with one string
wrapped around them; there need to be 2 strands of the string pulling up on the bottom pulley.
2. Measure and record the weight of the mass you will hang from the bottom pulley. Then hang
the mass on the pulley.
Weight = __________________
3. Measure the effort force you must exert in three situations:
a) Effort force with hanging mass at rest = __________________
b) Effort force with hanging mass being raised at constant velocity = ____________
c) Effort force with hanging mass being lowered at constant velocity = ___________
4. Give plausible reasons why the three effort forces you measured might not be equal.
5. Now suppose that you raise the hanging mass by 10 centimeters. Through how much distance
must you exert the effort force ? On your prelab diagram, clearly label the effort and load
distances for this situation, and write a short explanation of why those two distances are not
equal.
6. How much effort force would be required if your pulley were an ideal simple machine ? Justify
your answer in two ways:
a) Using a force diagram for the hanging mass and the fact that the string pulls with the
same force at all places, assuming that there is no friction with the pulleys. How does
Newton’s First Law apply here ?
b) Using the fact that for an ideal machine, the work done by the effort force equals the
work done by the load force
Analysis
7. Use your measurements to determine the following quantities. Show all work clearly. Pay particular
attention to the units and signs of all quantities. Also, be careful about using the correct effort and load
forces when raising and lowering.
a. Mechanical Advantage of your pulley system (while mass is being raised):
b. Ideal Mechanical Advantage of your pulley system:
c. Work Done by the Effort force in raising the mass 10 cm:
d. Work Done by the Effort force in lowering the mass 10 cm:
e. Work done by the Load force in raising the mass 10 cm:
f. Work done by the Load force in lowering the mass 10 cm:
g. Work done by gravity when you raised the mass 10 cm:
h. Work done by gravity when you lowered the mass 10 cm :
i. Efficiency of your pulley system (while mass is being raised):